DOCK8 deficiency is characterized by recurrent sinopulmonary infections, chronic viral skin infections, eosinophilia, and elevated IgE levels. DOCK8 patients are also predisposed to autoimmunity; they develop autoimmune hemolytic anemia, colitis, sclerosing colitis, and vasculitis. We found that DOCK8 deficiency in patients leads to the development of autoantibodies, and patients have decreased numbers of regulatory T (Treg) cells and impaired Treg cell in vitro suppressive activity (Janssen et al. J Allergy Clin Immunol (2014) in press). In addition, we have preliminary data that Dock8-/- mice develop autoantibodies and have impaired Treg numbers and in vitro suppressive ability. Furthermore, mice with a selective Dock8 deficiency in Foxp3 expressing Treg cells develop spontaneous splenomegaly and lymphadenopathy at an early age. Our overall hypothesis is that DOCK8 deficiency leads to the generation of autoreactive lymphocytes. We will test this hypothesis using mouse models, and when possible utilize samples from DOCK8 deficient patients to confirm our findings in humans. To test the hypothesis that Dock8 deficient mice develop autoimmune disease with aging, we will age Dock8-/- mice and do serial examinations for autoantibody production and signs of autoimmune disease. If Dock8-/- mice do not develop spontaneous autoimmune disease, we will look at inducing disease with TLR agonists. Simultaneously, we will examine Dock8-/- mice for accelerated disease in the context of autoimmune prone backgrounds. Next, we will examine the role of T and B cell intrinsic Dock8 deficiency in developing autoimmunity, using Dock8 conditional knock-out mice that have already been generated. Finally, we have preliminary data that Dock8 is important for Treg cell number and suppressive activity. We will examine the development, survival, and stability of Treg cells in Dock8 deficient mice and elucidate whether these defects are Treg cell intrinsic. In addition, using several in vivo models of autoimmunity/inflammation, we will test Dock8 deficient Treg cell suppressive function. Together, these studies should yield answers regarding the mechanism of developing of autoimmunity in DOCK8 deficient patients. We have generated Dock8 deficient mice in-house. The Dock8 locus in these mice have a mutation in exon 9 that mimics a nonsense mutation found in a DOCK8 deficient patient who does not express any DOCK8 protein. In addition, we have engineered Dock8flox/flox conditional knock-out mice. We have already bred these mice with Cd4-Cre and Foxp3-YFP-Cre mice to examine role of Dock8 in a T cell and Treg cell intrinsic manner. We are in the process of mating the Dock8flox/flox mice with mb-1-Cre to examine B cell intrinsic effects. These mice will allow us to examine cell intrinsic roles of Dock8 in the generation of autoantibodies and autoimmunity. We also have access to a unique cohort of DOCK8 deficient patients through participation in the International Consortium of Immunodeficiency (ICID). Often patients referred through the ICID are evaluated and treated at Boston Children's hospital, and this allows us to obtain blood samples for validation of our mouse findings. Here, we present promising data that forms the basis for this scientific application. Through the utilization of thee mouse models and patient samples, we should be able to delve into these questions in a meaningful way to explain the human disease. Dr. Janssen received her M.D. and Ph.D. in Immunology at Duke University. Her graduate studies focused on lymphocyte signaling. During her residency and fellowship, Dr. Janssen acquired training in clinical immunology and rheumatology. She is currently mentored by Dr. Raif Geha, Chief of Immunology, at Boston Children's Hospital. Under his guidance, Dr. Janssen published two first author manuscripts on lymphocyte subsets in DOCK8 deficient patients and the role of TLR4 in IgE class switching. In addition, she had two first author manuscripts recently accepted to the Journal of Allergy and Clinical Immunology on the development of autoimmunity and impaired regulatory T cells in DOCK8 and LRBA deficient patients. Successful funding of this K08 application will give Dr. Janssen the ability to continue these studies, as well as to further develop her career as a physician scientist. She will continue to have the opportunity to participate in the various career development opportunities provided by Boston Children's, the Harvard Medical School, and the Harvard Catalyst. Dr. Janssen's goal over the next five years is to progress to research independence under the guidance of her mentor, advisory committee, and the experienced faculty at Harvard Medical School. She would like to continue to draw from her clinical experience to explore new questions in autoimmunity and immune dysregulation.